This invention pertains to controlling and indicating the tilt and trim of the propeller carrying stern leg of a marine propulsion unit.
A typical stern leg with which the new control system may be used is one that is mounted on the transom of a boat for being driven about a vertical axis to steer the boat and about a horizontal axis to alter the attitude or angle of the propeller axis and thereby affect a change in th pitch or trim of the boat. Turning the stern leg about the horizontal axis through a large angle such as is sufficient to lift the propeller out of the water to clear an obstruction or for docking is characterized by the term "tilt." Turning the stern leg about the horizontal axis through a limited angle with the propeller remaining totally under water to set the attitude or level of the boat itself while it is underway is characterized as "trim." Customarily, manually operated control devices for selecting and determining tilt and trim are located within reach of the boat operator.
Hydraulic work cylinders are commonly interposed between the transom of the boat and the stern leg for turning the stern leg through the trim angle range, which may be between 0.degree. and about 25.degree. from vertical, and through the larger full lift or tilt angle range which may go up to about 45.degree. to 55.degree. from vertical. The hydraulic work cylinder also holds the stern leg at the selected angle. Hydraulic pressure for bidirectional operation of the hydraulic work cylinders can be obtained from a reversible pump driven by a reversible motor.
There are a variety of prior art systems for regulating trim angle. One system is described in U.S. Pat. No. 3,894,250. In this system, the operator sets a potentiometer at the operator control station to the desired trim angle as indicated by a calibrated scale. Another signal, indicative of the present angle of the stern leg, is derived from a sensor which turns with the stern leg. Whether the stern leg angle is greater or less than the manually set angle is determined by using operational amplifier comparators. If the trim angle called for by the manually set potentiometer is greater than the present angle of the stern leg sensor, an error signal of such polarity is produced as to cause a motor driving a hydraulic pump to turn in an appropriate direction for applying pressure to the proper side of the work cylinder piston to drive the stern leg until it agrees with the selected manual setting. If the stern leg is at a lesser angle than that which has been manually set, an error signal is produced having such polarity as to cause the pump motor to turn in the opposite direction and drive the stern leg until null is reached or the manually selected angle and the actual stern leg angle agree. Insofar as can be determined from the disclosure in the cited patent, the same manually settable control device would be used for causing the stern leg to be turned through one angular range for trim and a larger angular range for tilt. The alternative would be to have separate control circuits for tilt and trim functions. One cannot infer that there is anything present for inactivating the trim function if the stern leg is in its tilt angle range nor is it evident that using the tilt control would override the trim function. In other words, the tilt and trim functions are not mutually exclusive.
Another trim or tilt angle control system is disclosed in U.S. Pat. No. 3,797,449. It uses a bridge circuit which puts out an error signal until the difference between the manually selected tilt or trim angle and the present angle of the stern leg agree. One leg of the bridge circuit is constituted by an electromagnet coil that drives a meter for producing an indication of the stern angle at which null occurred. Tilting the stern leg with a hydraulic work cylinder is suggested in this patent. The work cylinder is pressurized with a hydraulic pump driven by a reversible motor. One push button switch is provided to the operator for raising the stern leg and another for lowering it. The push buttons, through appropriate circuitry, control the rotational direction of the reversible pump driving motor. The same control devices, namely, the push buttons are used for adjusting trim and tilt of the stern leg. If the operator maintains the stern raising or tilt up switch, the stern leg will be caused by swing through the maximum desired trim angle range and into the tilt range. The tilt and trim functions are not mutally exclusive.
Another prior system is shown in U.S. Pat. No. 3,641,965. In this case, three push buttons are provided, one for raising the stern leg during trimming, another for lowering it, and another that is used in combination with the first one to override a limit switch and let the stern leg angulate into the tilt angle range. The tilt and trim functions are, therefore, not mutually exclusive.
U.S. Pat. Nos. 3,662,243 and 3,739,738 illustrate marine propulsion device steering control circuits that compare a signal corresponding to the angle to which a steering wheel has been turned with a signal corresponding to the position of the steering unit. When a difference signal exists transistors are turned on and they control relays which cause the steering unit drive motor to run until the difference is nulled.